The continual scaling of semiconductor devices in recent years has driven the improvement of large scale integrated circuit (LSI) performance to a great extent. This is achieved by increasing the integrated density, that is, by miniaturizing the components such as transistors that build up the semiconductor devices. As a result, source/drain regions comprising shallow junctions with low resistance have become significant in reducing short channel effects which are brought about by the miniaturization of the components.
To form the shallow junction or shallow impurity diffusion layer, rapid thermal anneal (RTA) had been widely employed in the semiconductor fabrication industry. Impurity ions are implanted in a semiconductor substrate and are activated by annealing at a high temperature typically using a halogen lamp in a matter of seconds.
Nevertheless, the rapid decrease in the dimension of the semiconductor devices has demanded the formation of ultra shallow junctions which require better control of diffusion without compromising the activation rate of the impurities. Recently, anneals with even lower thermal budgets, such as a flash lamp anneal (FLA) at high temperatures in a duration of milliseconds, have been developed to meet the demand. The flash lamp is a gas discharge light source producing pulsed instantaneous radiation. Typically, one or more noble gases like xenon (Xe) or krypton (Kr) are filled in the bulb. The capacitor of the lamp which stores electrical charges can instantaneously discharge to emit a high intensity light within a few hundred μs to a few hundred ms.
FLA, however, which utilizes high irradiation energy for uniform activation of impurities, would result in a sudden temperature increase on the semiconductor substrate. The temperature difference in between a top surface and a bottom surface across the large substrate area could raise the amount of thermal stress which could result in the deformation of the substrate like wafer warpage and even wafer breakage.